A fixture for supporting a mercury vapor, metal halide or high pressure sodium lamp generally includes a housing for a capacitor and an igniter, a transformer, a socket for supporting the bulb and a reflector surrounding the bulb. If hung from a ceiling, electrical leads extend through a conduit into the upper housing for connection to the igniter and capacitor. These components connect to the transformer, which is in turn electrically connected to the socket, which is generally located below the transformer.
In operation, heat is generated by the energized bulb and the transformer. Because all of the components of the fixture are susceptible to excessive heat build up, and excessive heat can cause shorter useful life, or in some cases, a potential fire hazard, this heat must be dissipated. To reduce heat build up at the bulb, some fixtures have an annular open space between the top of the reflector and the socket. This open space causes a chimney effect which allows heat to rise upwardly and away from the bulb and socket, rather than being trapped within the otherwise closed upper end of the housing.
While this chimney effect alleviates heat build up at the bulb and socket, it increases the ambient temperature of operation for the transformer, the igniter and the capacitor located thereabove.
In rating light fixtures for safe operation at a particular ambient temperature, Underwriters' Laboratory requires that all of the components of the fixture dissipate heat sufficiently for the fixture to be qualified for operation at that temperature. Because the annular spacing between the reflector and the socket generally impairs the heat dissipation capability of the capacitor, igniter and transformer, the chimney effect is only a partial solution to heat build up problems. It limits the ability of a fixture as a whole to achieve a higher temperature rating.
It is a primary objective of this invention to provide a light fixture which, compared to prior fixtures, achieves a higher temperature rating, thereby to extend the useful life and enable safer operation of all the components at higher ambient temperatures.
In the design of an electric light fixture, a number of other factors must also be considered. These other factors include pleasing aesthetics, ease in mounting and rebulbing, versatility in lamp wattage and line voltage and variation in the light distribution pattern. Each of these other features affects heat buildup, or heat generation. Generally, the higher the wattage of the bulb or the voltage of the line, the greater the amount of heat generated within the fixture. The amount of heat generated also depends upon the structural relationship among the necessary light fixture components, i.e., the volume of space occupied by the light fixture components and the density of the components within the given volume. Additionally, while the vertical position of a light reflector with respect to the bulb generally determines the light distribution pattern, the bulb is supported by a fixture which also houses the electrical components, and the distance between these electrical components and the reflector directly affects heat buildup. In all instances, a light fixture must dissipate heat with sufficient rapidity so as not to present a fire hazard.
In an attempt to meet independent, objective heat dissipation standards, as set by Underwriters' Laboratories, many light fixture designs have sacrificed factors such as aesthetic quality, versatility in light distribution adjustment and ease in mounting, maintaining and rebulbing.
It is an object of this invention to provide an electric light fixture with high heat dissipation capability without sacrificing other performance factors.
It is another object of the invention to provide an electric light fixture with enhanced heat dissipation capability and aesthetic quality.
It is still another object of the invention to provide an electric light fixture with enhanced heat dissipation capability and good selectability in achieving a desired light distribution pattern.